1. Field of the Invention
The present invention relates to a microactuator control apparatus using shape memory alloy (SMA) elements activated by the application of thermal energy, either from a high temperature gas or an optical sources.
2. Description of the Related Art
Shape memory alloys, such as the well known nickel-titanium type, exhibit novel properties in which they exhibit the ability to return to a predetermined shape when heated. When a SMA is cold, or below its transformation temperature, it exhibits very low yield strength and can be deformed quite easily into any desired shape which it will retain. However, when heated above its transformation temperature it will undergo a change in crystal structure which causes it to return to its original shape. In the event the SMA encounters any resistance during this transformation, it can exert extremely large forces upon the resisting media.
Thus SMA materials have proven to be invaluable for remote actuation devices. Although many uses of SMA materials have been heretofore disclosed as actuator devices these prior art devices generally employ electrical energy as their means for activating the SMA elements. For example see U.S. Pat. Nos. 5,769,389; 5,410,290; 5,271,075; 5,024,497; 5,004,318; and 4,987,314. However, using the SMA material itself to produce resistance heating is not desirable as SMA materials exhibit low electrical resistance thereby requiring higher current flow than other more suitable resistance heating elements.